The 1.9 THz [CII] observations provide a powerful probe of warm diffuse clouds, because they can observe them in emission and are useful as a tracer of their molecular H2 not directly traced by CO or other means. HIFI observations of [CII] provide a high resolution of 12 arcsec, better than that for single dish CO (> 30 arcsec) maps, and much better than HI (>30 arcsec). Thus with HIFI we have an opportunity probe the small scale structures in diffuse clouds in the inner Galaxy at distances > 3 kpc. To study the structure of diffuse ISM gas at small scales we propose HIFI maps of 1.9 THz (158 micron) [CII] line emission in a selection of 16 lines of sight (LOSs) towards the inner Galaxy, which are also being observed as part of the GOT C+ survey of [CII] in the Galactic plane. GOT C+ provides mainly single point spectra without any spatial data. Maps of [CII] will constrain better the cloud properties and models when combining [CII] and HI data. The proposed OTF X map will be along the longitude and latitude centered on 18 selected GOT C+ LOS over a length of 3 arcmin in each direction, which is adequate enough to provide sufficient spatial information on the small scale structures at larger distances (>3 kpc) and to characterize the CII filling factor in the larger beams of the ancillary (HI, CO, and CI data). The [CI] 609 & 370micron and the 12CO(7-6) (which lies within the CI band) are excellent diagnostics of the physical conditions of transition clouds and PDRs. We will use the ratio of the [CI] lines to constrain the kinetic temperature and volume density of the CII/CI/CO transition zones in molecular clouds using radiative transfer codes. We also propose OTF X maps in both the [CI] lines for all CII target LOSs. We anticipate fully resolved structural data in [CII] on at least 300 velocity resolved clouds along with their [C...I] emissions. We request a total of 33.2 hrs of HIFI observing time.
Publication
Origin and z-distribution of Galactic diffuse [C II] emission . Velusamy T. et al. . Astronomy & Astrophysics, Volume 572, id.A45, 20 pp. . 572 . 10.1051\/0004-6361\/201424350 . 2014A&A...572A..45V ,
Instrument
HIFI_HifiMapping_load-raster
Temporal Coverage
2011-10-06T05:29:52Z/2012-10-13T06:08:43Z
Version
SPG v14.1.0
Mission Description
Herschel was launched on 14 May 2009! It is the fourth 'cornerstone' mission in the ESA science programme. With a 3.5 m Cassegrain telescope it is the largest space telescope ever launched. It is performing photometry and spectroscopy in approximately the 55-671 µm range, bridging the gap between earlier infrared space missions and groundbased facilities.
